feat(pipeline): add runnable artifact pipeline increment

[Change Nature]
- This commit adds the first runnable increment of the F# artifact
  pipeline: CLI, server, frontend bundle, stage fixture, and tests.
  It is feature work, not a bug fix.

[New Capability]
- CLI `run` executes the three-step Blender fixture through the process
  bridge and writes GLBs, step logs, events, and a manifest; `verify`
  validates a manifest without Blender.
- Server exposes run start, run-scoped SSE, artifact manifest/file
  routes, and serves the Fable frontend from its build output.
- Frontend starts runs, follows run-scoped SSE progress, and links the
  artifact manifest on completion.

[Implementation]
- Shared layer holds domain, run state, replay, and artifact contracts;
  Modeling holds the pipeline, 120s bridge timeout, and result-file
  protocol; stage/blender/fixture.py owns geometry in Python (bpy owns
  geometry, F# owns orchestration).
- Fable bundle is regenerated into public/ and copied by the server
  project; solution includes all projects with warnings-as-errors.
- README documents build, Fable, server, interpreter/env, fixture
  limitations, and current verification status.

[Impact]
- Verified: 40/40 solution tests pass; Release build 0 warnings/errors;
  real CLI run with bpy 5.0.1 produced 3 GLBs, 3 logs, and a
  verify-clean manifest; isolated-port server smoke flow succeeded.
- Not yet verified: browser end-to-end behavior and production
  fidelity. Artifacts and caches are gitignored.

1 files changed, 83 insertions, 0 deletions

diff --git a/tests/SomhairlesDream.Server.Tests/CoordinatorTests.fs b/tests/SomhairlesDream.Server.Tests/CoordinatorTests.fs
new file mode 100644
index 0000000..e9689bb
--- /dev/null
+++ b/tests/SomhairlesDream.Server.Tests/CoordinatorTests.fs
@@ -0,0 +1,83 @@
+module SomhairlesDream.Server.Tests.CoordinatorTests
+
+open System
+open System.IO
+open System.Threading
+open Xunit
+open SomhairlesDream.Modeling
+open SomhairlesDream.Server
+open SomhairlesDream.Shared
+
+let private ids : RunIds =
+    { ProjectId = "heritage-001"
+      RunId = "run-20260920-001"
+      BaseId = "heritage"
+      TargetId = "heritage-001" }
+
+let private withTempDirectory action =
+    let path = Path.Combine(Path.GetTempPath(), "somhairles-dream-server-" + Guid.NewGuid().ToString("N"))
+    Directory.CreateDirectory(path) |> ignore
+
+    try
+        action path
+    finally
+        if Directory.Exists(path) then
+            Directory.Delete(path, true)
+
+type private TestBridge() =
+    interface IArtifactBridge with
+        member _.Export(request, _) =
+            File.WriteAllBytes(request.GlbPath, [| 0x67uy; 0x6Cuy; 0x54uy; byte request.Step.Index |])
+            Directory.CreateDirectory(Path.GetDirectoryName(request.LogPath)) |> ignore
+            File.WriteAllText(request.LogPath, $"bridge log for {request.Step.StepId}")
+
+            Ok
+                { BlenderVersion = "5.0.1"
+                  ExportedAt = DateTimeOffset.Parse("2026-09-20T12:00:05Z")
+                  ObjectIds = request.Step.ObjectIds
+                  VerifiedObjectIds = request.Step.ObjectIds
+                  GlbBytes = 4L
+                  RenderPath = None
+                  RenderedAt = None }
+
+let private waitFor predicate =
+    let deadline = DateTime.UtcNow.AddSeconds(5.)
+    let mutable matched = predicate ()
+
+    while not matched && DateTime.UtcNow < deadline do
+        Thread.Sleep(10)
+        matched <- predicate ()
+
+    matched
+
+[<Fact>]
+let ``coordinator starts one shared pipeline and publishes its manifest`` () =
+    withTempDirectory (fun root ->
+        let clock () = DateTimeOffset.Parse("2026-09-20T12:00:00Z")
+        let coordinator =
+            ArtifactRunCoordinator(
+                root,
+                (fun () -> TestBridge() :> IArtifactBridge),
+                clock,
+                TimeSpan.FromSeconds 15.
+            )
+
+        match coordinator.Start(ids, false) with
+        | Error message -> failwith message
+        | Ok(Accepted snapshot) ->
+            Assert.Equal(ids.ProjectId, snapshot.ProjectId)
+            Assert.Equal(ids.RunId, snapshot.RunId)
+        | Ok(Conflict _) -> failwith "expected the first start to be accepted"
+
+        let completed =
+            waitFor (fun () ->
+                coordinator.TryFind(ids.ProjectId, ids.RunId)
+                |> Option.exists (fun store -> store.Snapshot().Status = "complete"))
+
+        Assert.True(completed)
+
+        match coordinator.Manifest(ids.ProjectId, ids.RunId) with
+        | Error failure -> failwith $"manifest lookup failed: {failure}"
+        | Ok manifest ->
+            Assert.Equal("complete", manifest.Status)
+            Assert.Equal(3, manifest.Steps.Length))